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Trinity was the first detonation of a
nuclear weapon A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission or atomic bomb) or a combination of fission and fusion reactions (thermonuclear weapon), producing a nuclear exp ...
, conducted by the
United States Army The United States Army (USA) is the primary Land warfare, land service branch of the United States Department of Defense. It is designated as the Army of the United States in the United States Constitution.Article II, section 2, clause 1 of th ...
at 5:29 a.m. MWT (11:29:21 GMT) on July 16, 1945, as part of the
Manhattan Project The Manhattan Project was a research and development program undertaken during World War II to produce the first nuclear weapons. It was led by the United States in collaboration with the United Kingdom and Canada. From 1942 to 1946, the ...
. The test was of an implosion-design
plutonium Plutonium is a chemical element; it has symbol Pu and atomic number 94. It is a silvery-gray actinide metal that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibits six allotropes and four ...
bomb, or "gadget", of the same design as the Fat Man bomb later detonated over Nagasaki, Japan, on August 9, 1945. Concerns about whether the complex Fat Man design would work led to a decision to conduct the first nuclear test. The code name "Trinity" was assigned by J. Robert Oppenheimer, the director of the
Los Alamos Laboratory The Los Alamos Laboratory, also known as Project Y, was a secret scientific laboratory established by the Manhattan Project and overseen by the University of California during World War II. It was operated in partnership with the United State ...
, possibly inspired by the poetry of
John Donne John Donne ( ; 1571 or 1572 – 31 March 1631) was an English poet, scholar, soldier and secretary born into a recusant family, who later became a clergy, cleric in the Church of England. Under Royal Patronage, he was made Dean of St Paul's, D ...
. The test, both planned and directed by
Kenneth Bainbridge Kenneth Tompkins Bainbridge (July 27, 1904 – July 14, 1996) was an American physicist at Harvard University who worked on cyclotron research. His accurate measurements of mass differences between nuclear isotopes allowed him to confirm Albert ...
, was conducted in the Jornada del Muerto desert about southeast of
Socorro, New Mexico Socorro (, ''Help:Pronunciation respelling key, sə-KOR-oh'') is a city in Socorro County, New Mexico, Socorro County in the U.S. state of New Mexico. It is in the Middle Rio Grande Valley AVA, Rio Grande Valley at an elevation of . At the 2020 ...
, on what was the Alamogordo Bombing and Gunnery Range (renamed the
White Sands Proving Ground White Sands Missile Range (WSMR) is a United States Army military testing area and firing range located in the US state of New Mexico. The range was originally established in 1941 as the Alamogordo Bombing and Gunnery Range, where the Trinity ( ...
just before the test). The only structures originally in the immediate vicinity were the McDonald Ranch House and its ancillary buildings, which scientists used as a laboratory for testing bomb components. Fears of a fizzle prompted construction of "Jumbo", a steel containment vessel that could contain the plutonium, allowing it to be recovered; but ultimately Jumbo was not used in the test. On May 7, 1945, a rehearsal was conducted, during which of high explosive spiked with radioactive isotopes was detonated. Some 425 people were present on the weekend of the Trinity test. In addition to Bainbridge and Oppenheimer, observers included
Vannevar Bush Vannevar Bush ( ; March 11, 1890 – June 28, 1974) was an American engineer, inventor and science administrator, who during World War II, World War II headed the U.S. Office of Scientific Research and Development (OSRD), through which almo ...
,
James Chadwick Sir James Chadwick (20 October 1891 – 24 July 1974) was an English nuclear physicist who received the Nobel Prize in Physics in 1935 for his discovery of the neutron. In 1941, he wrote the final draft of the MAUD Report, which inspired t ...
, James B. Conant, Thomas Farrell,
Enrico Fermi Enrico Fermi (; 29 September 1901 – 28 November 1954) was an Italian and naturalized American physicist, renowned for being the creator of the world's first artificial nuclear reactor, the Chicago Pile-1, and a member of the Manhattan Project ...
, Hans Bethe,
Richard Feynman Richard Phillips Feynman (; May 11, 1918 – February 15, 1988) was an American theoretical physicist. He is best known for his work in the path integral formulation of quantum mechanics, the theory of quantum electrodynamics, the physics of t ...
,
Isidor Isaac Rabi Israel Isidor Isaac Rabi (; ; July 29, 1898 – January 11, 1988) was an American nuclear physicist who received the Nobel Prize in Physics in 1944 for his discovery of nuclear magnetic resonance, which is used in magnetic resonance imaging. H ...
, Leslie Groves, Frank Oppenheimer, Geoffrey Taylor, Richard Tolman,
Edward Teller Edward Teller (; January 15, 1908 – September 9, 2003) was a Hungarian and American Theoretical physics, theoretical physicist and chemical engineer who is known colloquially as "the father of the hydrogen bomb" and one of the creators of ...
, and
John von Neumann John von Neumann ( ; ; December 28, 1903 – February 8, 1957) was a Hungarian and American mathematician, physicist, computer scientist and engineer. Von Neumann had perhaps the widest coverage of any mathematician of his time, in ...
. The Trinity bomb released the explosive energy of ± , and a large cloud of fallout. Thousands of people lived closer to the test than would have been allowed under guidelines adopted for subsequent tests, but no one living near the test was evacuated before or afterward. The test site was declared a
National Historic Landmark A National Historic Landmark (NHL) is a National Register of Historic Places property types, building, district, object, site, or structure that is officially recognized by the Federal government of the United States, United States government f ...
district in 1965 and listed on the
National Register of Historic Places The National Register of Historic Places (NRHP) is the Federal government of the United States, United States federal government's official United States National Register of Historic Places listings, list of sites, buildings, structures, Hist ...
the following year.


Background

The creation of
nuclear weapon A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission or atomic bomb) or a combination of fission and fusion reactions (thermonuclear weapon), producing a nuclear exp ...
s arose from the scientific and political developments of the 1930s. The decade saw many new discoveries about the nature of atoms, including the existence of
nuclear fission Nuclear fission is a reaction in which the nucleus of an atom splits into two or more smaller nuclei. The fission process often produces gamma photons, and releases a very large amount of energy even by the energetic standards of radioactiv ...
. The concurrent rise of
fascist Fascism ( ) is a far-right, authoritarian, and ultranationalist political ideology and movement. It is characterized by a dictatorial leader, centralized autocracy, militarism, forcible suppression of opposition, belief in a natural soci ...
governments in Europe led to a fear of a German nuclear weapon project, especially among scientists who were refugees from
Nazi Germany Nazi Germany, officially known as the German Reich and later the Greater German Reich, was the German Reich, German state between 1933 and 1945, when Adolf Hitler and the Nazi Party controlled the country, transforming it into a Totalit ...
and other fascist countries. When their calculations showed that nuclear weapons were theoretically feasible, the British and United States governments supported an all-out effort to build them. These efforts were transferred to the authority of the U.S. Army in June 1942 and became the
Manhattan Project The Manhattan Project was a research and development program undertaken during World War II to produce the first nuclear weapons. It was led by the United States in collaboration with the United Kingdom and Canada. From 1942 to 1946, the ...
. Brigadier General Leslie R. Groves, Jr. was appointed its director in September. The weapons development portion of this project was located at the
Los Alamos Laboratory The Los Alamos Laboratory, also known as Project Y, was a secret scientific laboratory established by the Manhattan Project and overseen by the University of California during World War II. It was operated in partnership with the United State ...
in northern
New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...
, under the directorship of physicist J. Robert Oppenheimer. The
University of Chicago The University of Chicago (UChicago, Chicago, or UChi) is a Private university, private research university in Chicago, Illinois, United States. Its main campus is in the Hyde Park, Chicago, Hyde Park neighborhood on Chicago's South Side, Chic ...
,
Columbia University Columbia University in the City of New York, commonly referred to as Columbia University, is a Private university, private Ivy League research university in New York City. Established in 1754 as King's College on the grounds of Trinity Churc ...
and the Radiation Laboratory at the
University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California), is a Public university, public Land-grant university, land-grant research university in Berkeley, California, United States. Founded in 1868 and named after t ...
conducted other development work. Manhattan Project scientists had identified two fissile isotopes for potential use in bombs:
uranium-235 Uranium-235 ( or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exists in nat ...
and
plutonium-239 Plutonium-239 ( or Pu-239) is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 is also used for that purpose. Plutonium-239 is also one of the three main iso ...
. Uranium-235 became the basis of the Little Boy bomb design, first used (without prior testing) in the bombing of Hiroshima; the design used in the Trinity test, and eventually used in the bombing of Nagasaki ( Fat Man), was based on plutonium. The original design considered for a weapon based on plutonium-239 was Thin Man, in which (as in the Little Boy uranium bomb) two subcritical masses of fissile material would be brought rapidly together to form a single critical mass. Plutonium is a
synthetic element A synthetic element is a known chemical element that does not occur naturally on Earth: it has been created by human manipulation of fundamental particles in a nuclear reactor, a particle accelerator, or the explosion of an atomic bomb; thus, it i ...
with complicated properties about which little was known at first, as until 1944 it had been produced only in
cyclotron A cyclotron is a type of particle accelerator invented by Ernest Lawrence in 1929–1930 at the University of California, Berkeley, and patented in 1932. Lawrence, Ernest O. ''Method and apparatus for the acceleration of ions'', filed: Januar ...
s in very pure microgram amounts, whereas a weapon would require kilogram quantities bred in a reactor. In April 1944, Los Alamos physicist Emilio Segrè discovered that plutonium produced by the X-10 Graphite Reactor at Clinton Engineer Works contained
plutonium-240 Plutonium-240 ( or Pu-240) is an isotope of plutonium formed when plutonium-239 captures a neutron. The detection of its spontaneous fission led to its discovery in 1944 at Los Alamos and had important consequences for the Manhattan Project. ...
as an impurity. Plutonium-240 undergoes
spontaneous fission Spontaneous fission (SF) is a form of radioactive decay in which a heavy atomic nucleus splits into two or more lighter nuclei. In contrast to induced fission, there is no inciting particle to trigger the decay; it is a purely probabilistic proc ...
at thousands of times the rate of plutonium-239, and the extra
neutron The neutron is a subatomic particle, symbol or , that has no electric charge, and a mass slightly greater than that of a proton. The Discovery of the neutron, neutron was discovered by James Chadwick in 1932, leading to the discovery of nucle ...
s thereby released made it likely that plutonium in a gun-type fission weapon would detonate too soon after a critical mass was formed, producing a " fizzle"—a nuclear explosion many times smaller than a full explosion. The Thin Man design would therefore not work. Project scientists then turned to a more technically difficult implosion design. In September 1943, mathematician
John von Neumann John von Neumann ( ; ; December 28, 1903 – February 8, 1957) was a Hungarian and American mathematician, physicist, computer scientist and engineer. Von Neumann had perhaps the widest coverage of any mathematician of his time, in ...
had proposed surrounding a fissile "core" by two different
high explosives An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An exp ...
which produced
shock wave In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a me ...
s of different speeds. Alternating the faster- and slower-burning explosives in a carefully calculated configuration would produce a compressive wave upon their simultaneous detonation. This so-called " explosive lens" focused the shock waves inward with sufficient force to rapidly compress the solid plutonium core to several times its original density. The increase in density caused the core previously subcriticalto become supercritical. At the same time, the shock wave activated a small
neutron source A neutron source is any device that emits neutrons, irrespective of the mechanism used to produce the neutrons. Neutron sources are used in physics, engineering, medicine, nuclear weapons, petroleum exploration, biology, chemistry, and nuclear p ...
at the center of the core, thereby assuring that the
chain reaction A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback leads to a self-amplifying chain of events. Chain reactions are one way that sys ...
would begin in earnest immediately at the moment of compression. Such a complicated design required substantial research and experimentation in engineering and
hydrodynamics In physics, physical chemistry and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids – liquids and gases. It has several subdisciplines, including (the study of air and other gases in ...
, and in August 1944 the entire Los Alamos Laboratory was reorganized to focus on this work.


Preparation


Decision

The idea of testing the implosion device was brought up in discussions at Los Alamos in January 1944 and attracted enough support for Oppenheimer to approach Groves. Groves gave approval, but he had concerns. The Manhattan Project had spent a great deal of money and effort to produce the plutonium, and he wanted to know whether there would be a way to recover it. The Laboratory's Governing Board then directed Norman Ramsey to investigate how this could be done. In February 1944, Ramsey proposed a small-scale test in which the explosion was limited in size by reducing the number of generations of chain reactions, and that it take place inside a sealed containment vessel from which the plutonium could be recovered. The means of generating such a controlled reaction were uncertain, and the data obtained would not be as useful as that from a full-scale explosion. Oppenheimer argued that the bomb "must be tested in a range where the energy release is comparable with that contemplated for final use." In March 1944, he obtained Groves's tentative approval for testing a full-scale explosion inside a containment vessel, although Groves was still worried about how he would explain the loss of "a billion dollars worth" of plutonium in the event the test failed.


Code name

The origin of the code name "Trinity" for the test is unknown, but it is often attributed to Oppenheimer as a reference to the poetry of
John Donne John Donne ( ; 1571 or 1572 – 31 March 1631) was an English poet, scholar, soldier and secretary born into a recusant family, who later became a clergy, cleric in the Church of England. Under Royal Patronage, he was made Dean of St Paul's, D ...
, which in turn references the Christian belief of the
Trinity The Trinity (, from 'threefold') is the Christian doctrine concerning the nature of God, which defines one God existing in three, , consubstantial divine persons: God the Father, God the Son (Jesus Christ) and God the Holy Spirit, thr ...
. In 1962, Groves wrote to Oppenheimer about the origin of the name, asking if he had chosen it because it was a name common to rivers and peaks in the West and would not attract attention, and elicited this reply:


Organization

In March 1944, planning for the test was assigned to
Kenneth Bainbridge Kenneth Tompkins Bainbridge (July 27, 1904 – July 14, 1996) was an American physicist at Harvard University who worked on cyclotron research. His accurate measurements of mass differences between nuclear isotopes allowed him to confirm Albert ...
, a professor of physics at
Harvard University Harvard University is a Private university, private Ivy League research university in Cambridge, Massachusetts, United States. Founded in 1636 and named for its first benefactor, the History of the Puritans in North America, Puritan clergyma ...
, working under explosives expert George Kistiakowsky. Bainbridge's group was known as the E-9 (Explosives Development) Group. Stanley Kershaw, formerly from the National Safety Council, was made responsible for safety.
Captain Captain is a title, an appellative for the commanding officer of a military unit; the supreme leader or highest rank officer of a navy ship, merchant ship, aeroplane, spacecraft, or other vessel; or the commander of a port, fire or police depa ...
Samuel P. Davalos, the assistant post engineer at Los Alamos, was placed in charge of construction.
First Lieutenant First lieutenant is a commissioned officer military rank in many armed forces; in some forces, it is an appointment. The rank of lieutenant has different meanings in different military formations, but in most forces it is sub-divided into a se ...
Harold C. Bush became commander of the Base Camp at Trinity. Scientists William Penney, Victor Weisskopf and Philip Moon were consultants. Eventually seven subgroups were formed: * TR-1 (Services) under John H. Williams * TR-2 (Shock and Blast) under John H. Manley * TR-3 (Measurements) under Robert R. Wilson * TR-4 (Meteorology) under J. M. Hubbard * TR-5 (Spectrographic and Photographic) under Julian E. Mack * TR-6 (Airborne Measurements) under Bernard Waldman * TR-7 (Medical) under Louis H. Hempelmann The E-9 group was renamed the X-2 (Development, Engineering and Tests) Group in the August 1944 reorganization.


Test site

Safety and security required a remote, isolated and unpopulated area. The scientists also wanted a flat area to minimize secondary effects of the blast, and with little wind to spread radioactive fallout. Eight candidate sites were considered: the Tularosa Valley; the Jornada del Muerto Valley; the area southwest of
Cuba, New Mexico Cuba is a village in Sandoval County, New Mexico, Sandoval County, New Mexico, United States. As of the United States Census, 2010, 2010 census, the village population was 735. It is part of the Albuquerque, New Mexico, Albuquerque Albuquerque m ...
, and north of Thoreau; and the lava flats of the El Malpais National Monument, all in New Mexico; the San Luis Valley near the Great Sand Dunes National Monument in Colorado; the Desert Training Area and San Nicolas Island in Southern California; and the sand bars of
Padre Island Padre Island is the largest of the Texas barrier islands and the world's longest barrier island. The island is located along Texas's southern coast of the Gulf of Mexico and is noted for its white sandy beaches. Meaning ''father'' in Spanish, ...
, Texas. The sites were surveyed by car and by air by Bainbridge, R. W. Henderson, Major W. A. Stevens and Major Peer de Silva. The site finally chosen, after consulting with Major General
Uzal Ent Uzal Girard Ent CBE (March 3, 1900 – March 5, 1948) was an American United States Army Air Forces, Army Air Forces officer who served as the commander of the Second Air Force during World War II. Early life and education Ent was born on ...
, the commander of the Second Air Force on September 7, 1944, lay at the northern end of the Alamogordo Bombing Range, in Socorro County near the towns of Carrizozo and
San Antonio San Antonio ( ; Spanish for " Saint Anthony") is a city in the U.S. state of Texas and the most populous city in Greater San Antonio. San Antonio is the third-largest metropolitan area in Texas and the 24th-largest metropolitan area in the ...
(). The Alamogordo Bombing Range was renamed the White Sands Proving Ground on July 9, 1945, one week before the test. Despite the criterion that the site be isolated, nearly half a million people lived within of the test site; soon after the Trinity test, the Manhattan Project's chief medical officer, Colonel Stafford L. Warren, recommended that future tests be conducted at least 150 miles from populated areas. The only structures in the vicinity were the McDonald Ranch House and its ancillary buildings, about to the southeast. Like the rest of the Alamogordo Bombing Range, it had been acquired by the government in 1942. The patented land had been condemned and grazing rights suspended. Scientists used this as a laboratory for testing bomb components. Bainbridge and Davalos drew up plans for a base camp with accommodation and facilities for 160 personnel, along with the technical infrastructure to support the test. A construction firm from
Lubbock, Texas Lubbock ( ) is a city in the U.S. state of Texas and the county seat of Lubbock County. With a population of 272,086 in 2024, Lubbock is the 10th-most populous city in Texas and the 84th-most populous in the United States. The city is in the ...
, built the barracks, officers' quarters, mess hall and other basic facilities. The requirements expanded and by July 1945 250 people worked at the Trinity test site. On the weekend of the test, there were 425 present. Lieutenant Bush's twelve-man MP unit arrived at the site from Los Alamos on December 30, 1944. This unit established initial security checkpoints and horse patrols. The distances around the site proved too great for the horses, so they were repurposed for
polo Polo is a stick and ball game that is played on horseback as a traditional field sport. It is one of the world's oldest known team sports, having been adopted in the Western world from the game of Chovgan (), which originated in ancient ...
playing, and the MPs resorted to using jeeps and trucks for transportation. Maintenance of morale among men working long hours under harsh conditions along with dangerous reptiles and insects was a challenge. Bush strove to improve the food and accommodation and to provide organized games and nightly movies. Throughout 1945, other personnel arrived at the Trinity Site to help prepare for the bomb test. They tried to use water out of the ranch wells, but found the water so
alkaline In chemistry, an alkali (; from the Arabic word , ) is a basic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The ...
, it was not drinkable. They were forced to use U.S. Navy saltwater soap and hauled drinking water in from the firehouse in Socorro. Gasoline and diesel were purchased from the
Standard Oil Standard Oil Company was a Trust (business), corporate trust in the petroleum industry that existed from 1882 to 1911. The origins of the trust lay in the operations of the Standard Oil of Ohio, Standard Oil Company (Ohio), which had been founde ...
plant there. Freshwater was trucked in, per load, from away. Military and civilian construction personnel built warehouses, workshops, a magazine and commissary. The railroad siding at Pope, New Mexico, was upgraded by adding an unloading platform. Roads were built, and of telephone wire were strung. Electricity was supplied by portable generators. Bomb shelters to protect test observers were the most expensive to construct. Due to its proximity to the bombing range, the base camp was accidentally bombed twice in May. When the lead plane on a practice night raid accidentally knocked out the generator or otherwise doused the lights illuminating their target, they went in search of the lights, and since they had not been informed of the presence of the Trinity base camp, and it was lit, they bombed it instead. The accidental bombing damaged the stables and the carpentry shop, and a small fire resulted.


Jumbo

Responsibility for the design of a containment vessel for an unsuccessful explosion, known as "Jumbo", was assigned to Robert W. Henderson and Roy W. Carlson of the Los Alamos Laboratory's X-2A Section. The bomb would be placed into the heart of Jumbo, and if the bomb's detonation was unsuccessful the walls of Jumbo would not be breached, making it possible to recover the bomb's plutonium. Hans Bethe, Victor Weisskopf, and Joseph O. Hirschfelder made the initial calculations, followed by a more detailed analysis by Henderson and Carlson. They drew up specifications for a steel sphere in diameter, weighing and capable of handling a pressure of . After consulting with the steel companies and the railroads, Carlson produced a scaled-back cylindrical design that would be much easier to manufacture. Carlson identified a company that normally made boilers for the Navy,
Babcock & Wilcox Babcock & Wilcox Enterprises, Inc. is an American energy technology and service provider that is active and has operations in many international markets with its headquarters in Akron, Ohio. Historically, the company is best known for their stea ...
; they had made something similar and were willing to attempt its manufacture. As delivered in May 1945, Jumbo was in diameter and long with walls thick, and weighed . A special train brought it from the Babcock & Wilcox plant in
Barberton, Ohio Barberton is a city in Summit County, Ohio, Summit County, Ohio, United States. The population was 25,191 at the 2020 United States census, 2020 census. Located directly southwest of Akron, Ohio, Akron, it is a suburb of the Akron metropolitan are ...
, to the siding at Pope, where it was loaded on a large trailer and towed across the desert by crawler tractors. At the time, it was the heaviest item ever shipped by rail. For many of the Los Alamos scientists, Jumbo was "the physical manifestation of the lowest point in the Laboratory's hopes for the success of an implosion bomb." By the time it arrived, the reactors at the Hanford Engineer Works produced plutonium in quantity, and Oppenheimer was confident that there would be enough for a second test. The use of Jumbo would interfere with the gathering of data on the explosion, the primary objective of the test. An explosion of more than would vaporize the steel and make it difficult to measure the thermal effects. Even would send fragments flying, presenting a hazard to personnel and measuring equipment. It was therefore decided not to use it. Instead, it was hoisted up a steel tower from the explosion, where it could be used for a subsequent test. In the end, Jumbo survived the explosion, although its tower did not. Jumbo was destroyed on April 16, 1946, when an Army ordnance team detonated eight 500 lb bombs in the bottom of the steel container. Jumbo, with its steel banding around the middle, had been designed to contain the 5,000 lbs of high explosive in the atomic bomb while it was suspended in the center of the vessel. With the conventional bombs placed in the bottom of Jumbo, the resulting blast sent fragments flying in all directions as far as three quarters of a mile. Who authorized the destruction of Jumbo remains controversial. The rusting skeleton of Jumbo sits in the parking lot at the Trinity site on the White Sands Missile Range, where it was moved in 1979. The development team also considered other methods of recovering active material in the event of a dud explosion. One idea was to cover it with a cone of sand. Another was to suspend the bomb in a tank of water. As with Jumbo, it was decided not to proceed with these means of containment. The (Chemistry and Metallurgy) group at Los Alamos also studied how the active material could be chemically recovered after a contained or failed explosion.


100-ton test

Because there would be only one chance to carry out the test correctly, Bainbridge decided that a rehearsal should be carried out to allow the plans and procedures to be verified, and the instrumentation to be tested and calibrated. Oppenheimer was initially skeptical but gave permission, and he later agreed that it contributed to the success of the Trinity test. A wooden platform was constructed to the southeast of Trinity
ground zero A hypocenter or hypocentre (), also called ground zero or surface zero, is the point on the Earth's surface directly below a nuclear explosion, meteor air burst, or other mid-air explosion. In seismology, the hypocenter of an earthquake is its p ...
. The high explosive was piled in its wooden shipping boxes in the shape of a pseudo-octagonal prism on it. The charge consisted of tons of TNT and tons of
Composition B Composition B (Comp B), also known as Hexotol and Hexolite (among others), is a high explosive consisting of castable mixtures of RDX and TNT. It is used as the main explosive filling in artillery projectiles, rockets, land mines, hand grenade ...
(with the total explosive power of approximately ), actually a few tons more than the stated "100-tons". Kistiakowsky assured Bainbridge that the explosives used were not susceptible to shock. This was proven correct when some boxes fell off the elevator lifting them up to the platform. Flexible tubing was threaded through the pile of boxes of explosives. A radioactive slug from Hanford with of beta ray activity and of
gamma ray A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...
activity was dissolved, and Hempelmann poured the solution into the tubing. The test was scheduled for May 5 but was postponed for two days to allow for more equipment to be installed. Requests for further postponements had to be refused because they would have affected the schedule for the main test. The detonation time was set for 04:00 Mountain War Time (MWT), on May 7, but there was a 37-minute delay to allow the observation plane, a
Boeing B-29 Superfortress The Boeing B-29 Superfortress is a retired American four-engined propeller-driven heavy bomber, designed by Boeing and flown primarily by the United States during World War II and the Korean War. Named in allusion to its predecessor, the Bo ...
from the 216th Army Air Forces Base Unit flown by Major Clyde "Stan" Shields, to get into position. The fireball of the conventional explosion was visible from Alamogordo Army Air Field away, but there was little shock at the base camp away. Shields thought that the explosion looked "beautiful", but it was hardly felt at . Herbert L. Anderson practiced using a converted
M4 Sherman The M4 Sherman, officially medium tank, M4, was the medium tank most widely used by the United States and Western Allies in World War II. The M4 Sherman proved to be reliable, relatively cheap to produce, and available in great numbers. I ...
tank lined with lead to approach the and blast crater and take a soil sample, although the radioactivity was low enough to allow several hours of unprotected exposure. An electrical signal of unknown origin caused the explosion to go off 0.25 seconds early, ruining experiments that required split-second timing. The
piezoelectric Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied stress (mechanics), mechanical s ...
gauges developed by Anderson's team correctly indicated an explosion of 108 tons of TNT, but Luis Walter Alvarez, Luis Alvarez and Waldman's airborne condenser gauges were far less accurate. In addition to uncovering scientific and technological issues, the rehearsal test revealed practical concerns as well. Over 100 vehicles were used for the rehearsal test, but it was realized more would be required for the main test, and they would need better roads and repair facilities. More radios and more telephone lines were required. Lines needed to be buried to prevent damage by vehicles. A Teleprinter, teletype was installed to allow better communication with Los Alamos. A town hall was built to allow for large conferences and briefings, and the mess hall had to be upgraded. Because dust thrown up by vehicles interfered with some of the instrumentation, of road was sealed.


The bomb

The term "gadget"—a laboratory euphemism for a bomb—gave the laboratory's weapon physics division, "G Division", its name in August 1944. At that time it did not refer specifically to the Trinity Test device as that had yet to be developed, but once it was, it became the laboratory code name. The Trinity bomb was officially a Y-1561 device, as was the Fat Man used later in the bombing of Nagasaki. The two were very similar, though the Trinity bomb lacked fuzing and external ballistic casing. The bombs were still under development, and small changes continued to be made to the Fat Man design. To keep the design as simple as possible, a nearly solid spherical core was chosen rather than a hollow one, although calculations showed that a hollow core would be more efficient in its use of plutonium. The core was compressed to prompt critical, prompt super-criticality by the implosion generated by the high explosive lens. This design became known as a "Christy Core" or "Pit (nuclear weapon)#Christy pits, Christy pit" after physicist Robert F. Christy, who made the solid pit design a reality after it was initially proposed by
Edward Teller Edward Teller (; January 15, 1908 – September 9, 2003) was a Hungarian and American Theoretical physics, theoretical physicist and chemical engineer who is known colloquially as "the father of the hydrogen bomb" and one of the creators of ...
. Of the several allotropes of plutonium, the metallurgists preferred the malleable δ (Delta (letter), delta) Phase (matter), phase. This was stabilized at room temperature by alloying it with 5% gallium. Two equal hemispheres of plutonium-gallium alloy were plated with silver, and designated by serial numbers HS-1 and HS-2. The radioactive core generated 15 W of heat, which warmed it up to about , and the silver plating developed blisters that had to be filed down and covered with gold foil; later cores were plated with nickel instead. A trial assembly of the bomb, without active components or explosive lenses, was carried out by the bomb assembly team headed by Norris Bradbury at Los Alamos on July 3. It was driven to Trinity and back. A set of explosive lenses arrived on July 7, followed by a second set on July 10. Each was examined by Bradbury and Kistiakowsky, and the best ones were selected for use. The remainder were handed over to Edward Creutz, who conducted a test detonation at Pajarito Canyon near Los Alamos without nuclear material. Magnetic measurements from this test suggested that the implosion might be insufficiently simultaneous and the bomb would fail. Bethe worked through the night to assess the results and reported that they were consistent with a perfect explosion. Assembly of the nuclear capsule began on July 13 at the McDonald Ranch House, where the master bedroom had been turned into a clean room. The polonium-beryllium Urchin (detonator), "Urchin" initiator was assembled, and Louis Slotin placed it inside the two hemispheres of the plutonium core. Cyril Stanley Smith, Cyril Smith then placed the core in the natural uranium tamper (nuclear weapon), tamper plug, or "slug". Air gaps were filled with gold foil, and the two halves of the plug were held together with uranium washers and screws which fit smoothly into the domed ends of the plug. To better understand the likely effect of a bomb dropped from a plane and detonated in air, and generate less nuclear fallout, the bomb was to be detonated atop a steel tower. The bomb was driven to the base of the tower, where a temporary eye bolt was screwed into the capsule and a Hoist (device), chain hoist was used to lower the capsule into the bomb. As the capsule entered the hole in the uranium tamper, it stuck. Robert Bacher realized that the heat from the plutonium core had caused the capsule to expand, while the explosives assembly with the tamper had cooled during the night in the desert. By leaving the capsule in contact with the tamper, the temperatures equalized and, in a few minutes, the capsule had slipped completely into the tamper. The eye bolt was then removed from the capsule and replaced with a threaded uranium plug, a boron disk was placed on top of the capsule (to complete the thin spherical shell of plastic boron around the tamper), an aluminum plug was screwed into the hole in the pusher (aluminum shell surrounding the tamper), and the two remaining high explosive lenses were installed. Finally, the upper Duralumin, Dural polar cap was bolted into place. The assembly of active material and high explosives was finished at 17:45 hours on 13 July. The gadget was hoisted to the top of the tower. The tower stood on four legs extending into the ground, with concrete footings. Atop it was an oak platform and a corrugated iron shack open to the west. The gadget was hauled up with an electric winch. A truckload of mattresses was placed underneath in case the cable broke and the gadget fell. A crew then attached each of the 32 Model 1773 Exploding-bridgewire detonator, EBW detonators. Full assembly of the bomb was completed by 17:00 on July 14. The seven-man arming party, consisting of Bainbridge, Kistiakowsky, Joseph McKibben and four soldiers including Lieutenant Bush, drove out to the tower to perform the final arming shortly after 22:00 on July 15.


Personnel

In the final two weeks before the test, some 250 personnel from Los Alamos were at work at the Trinity Site, and Lieutenant Bush's command had ballooned to 125 men guarding and maintaining the base camp. Another 160 men under Major T.O. Palmer were stationed outside the area with vehicles to evacuate the civilian population in the surrounding region should that prove necessary. They had enough vehicles to move 450 people to safety and had food and supplies to last them for two days. Arrangements were made for Alamogordo Army Air Field to provide accommodation. Groves warned Governor of New Mexico John J. Dempsey that martial law might have to be declared in the southwestern part of the state. Shelters were established due north, west, and south of the tower, each with its own chief: Robert Wilson at N-10,000, John Manley at W-10,000 and Frank Oppenheimer at S-10,000. Many other observers were around away, and some others were scattered at different distances, some in more informal situations.
Richard Feynman Richard Phillips Feynman (; May 11, 1918 – February 15, 1988) was an American theoretical physicist. He is best known for his work in the path integral formulation of quantum mechanics, the theory of quantum electrodynamics, the physics of t ...
claimed to be the only person to see the explosion without the goggles provided, relying on a truck windshield to screen out harmful ultraviolet wavelengths. Bainbridge asked Groves to keep his VIP list down to ten. He chose himself, Oppenheimer, Richard Tolman,
Vannevar Bush Vannevar Bush ( ; March 11, 1890 – June 28, 1974) was an American engineer, inventor and science administrator, who during World War II, World War II headed the U.S. Office of Scientific Research and Development (OSRD), through which almo ...
, James Bryant Conant, James Conant, Brigadier General Thomas F. Farrell, Charles Lauritsen,
Isidor Isaac Rabi Israel Isidor Isaac Rabi (; ; July 29, 1898 – January 11, 1988) was an American nuclear physicist who received the Nobel Prize in Physics in 1944 for his discovery of nuclear magnetic resonance, which is used in magnetic resonance imaging. H ...
, Sir Geoffrey Taylor, and Sir
James Chadwick Sir James Chadwick (20 October 1891 – 24 July 1974) was an English nuclear physicist who received the Nobel Prize in Physics in 1935 for his discovery of the neutron. In 1941, he wrote the final draft of the MAUD Report, which inspired t ...
. The VIPs viewed the test from Compania Hill (also called Compaña Hill or Cerro de la Colorado), about northwest of the tower. Photographic film was placed in nearby towns to detect radioactive contamination, and seismographs were placed in Tucson, Denver, and Chihuahua City, Chihuahua, Mexico to determine how far the explosion could be sensed. Calculations stated that even if the mechanical and electrical systems did not fail, the likelihood of a non-optimal test was greater than 10%. The observers set up a betting pool on the results of the test. Teller was the most optimistic, predicting . He wore gloves to protect his hands and sunglasses underneath the welding goggles that the government had supplied everyone with. He was one of the few scientists to watch the test (with eye protection), instead of following orders to lie on the ground with his back turned. He also brought suntan lotion, which he shared with the others. Ramsey chose zero (a complete dud), Robert Oppenheimer chose , Kistiakowsky , and Bethe chose . Rabi, the last to arrive, took the only remaining choice, which turned out to be the winner. Bethe later stated that his choice of 8 kt was exactly the value calculated by Segrè, and he was swayed by Segrè's authority over that of a more junior [but unnamed] member of Segrè's group who had calculated 20 kt.
Enrico Fermi Enrico Fermi (; 29 September 1901 – 28 November 1954) was an Italian and naturalized American physicist, renowned for being the creator of the world's first artificial nuclear reactor, the Chicago Pile-1, and a member of the Manhattan Project ...
offered to take wagers among the top physicists and military present on whether the atmosphere would ignite, and if so whether it would destroy just the state or incinerate the entire planet. This last result had been previously calculated by Bethe to be almost impossible, although for a while it had caused some of the scientists some anxiety. Bainbridge was furious with Fermi for frightening the guards, some of whom asked to be relieved; his own biggest fear was that nothing at all would happen, in which case he would have to return to the tower to investigate.


Explosion


Detonation

The scientists wanted good visibility, low humidity, light winds at low altitude, and westerly winds at high altitude for the test. The best weather was predicted between July 18 and 21, but the Potsdam Conference was due to start on July 16 and President Harry S. Truman wanted the test to be conducted before the conference began. It was therefore scheduled for July 16, the earliest date at which the bomb components would be available. The detonation was initially planned for 04:00 MWT but was postponed because of rain and lightning from early that morning. It was feared that the danger from radiation and fallout would be increased by rain, and lightning had the scientists concerned about a premature detonation, as had happened with a model of the electrical system. A crucial favorable weather report came in at 04:45, and the final twenty-minute countdown began at 05:10, read by Samuel King Allison, Samuel Allison. A rocket launched at 5:25 to signal five minutes before detonation; another rocket fired at 5:29. At 5:29:15, a switch in the control bunker started the detonation timer. By 05:30 the rain had gone. There were some communication problems: the shortwave radio frequency for communicating with the B-29s was shared with the Voice of America, and the FM radios shared a frequency with a railroad freight yard in San Antonio, Texas. Two circling B-29s observed the test, with Shields again flying the lead plane. They carried members of Project Alberta who would carry out airborne measurements during the atomic missions. These included Captain (United States O-6), Captain Deak Parsons, the associate director of the Los Alamos Laboratory and the head of Project Alberta; Luis Walter Alvarez, Luis Alvarez, Harold Agnew, Bernard Waldman, Wolfgang Panofsky, and William Penney. The overcast sky obscured their view of the test site. At 05:29:21 MWT (11:29:21 GMT) ± 15 seconds, the device exploded with an energy equivalent to . The desert sand, largely made of silica, melted and became a mildly radioactive light green glass, which was named trinitite. The explosion created a crater approximately deep and wide. The radius of the trinitite layer was approximately . The 100-foot shot tower was completely vaporized. At the time of detonation, the surrounding mountains were illuminated "brighter than daytime" for one to two seconds, and the heat was reported as "being as hot as an oven" at the base camp. The observed colors of the illumination changed from purple to green and eventually to white. The roar of the shock wave took 40 seconds to reach the observers. It was felt over away, and the mushroom cloud reached in height. Many observers recalled their amazement at the light from the explosion. Conant wrote, "The enormity of the light and its length quite stunned me". Lawrence, away, wrote of being "enveloped with a warm brilliant yellow white light—from darkness to brilliant sunshine in an instant". Ralph Carlisle Smith, watching from Compania Hill, wrote: Mary Argo was the only female staff member to be officially invited to watch the test. Joan Hinton snuck in to watch the test despite not being invited:
It was like being at the bottom of an ocean of light. We were bathed in it from all directions. The light withdrew into the bomb as if the bomb sucked it up. Then it turned purple and blue and went up and up and up. We were still talking in whispers when the cloud reached the level where it was struck by the rising sunlight so it cleared out the natural clouds. We saw a cloud that was dark and red at the bottom and daylight on the top. Then suddenly the sound reached us. It was very sharp and rumbled and all the mountains were rumbling with it. We suddenly started talking out loud and felt exposed to the whole world.
In his official report on the test, Thomas Farrell (who initially exclaimed, "The long-hairs have let it get away from them!") wrote: William L. Laurence of ''The New York Times'' had been transferred temporarily to the Manhattan Project at Groves's request in early 1945. Groves had arranged for Laurence to view significant events, including Trinity and the atomic bombing of Japan. Laurence wrote press releases with the help of the Manhattan Project's public relations staff. He later recalled: After the initial euphoria of witnessing the explosion had passed, Bainbridge told Oppenheimer, "Now we are all sons of bitches." Rabi noticed Oppenheimer's reaction: "I'll never forget his walk"; Rabi recalled, "I'll never forget the way he stepped out of the car ... his walk was like ''High Noon'' ... this kind of strut. He had done it." Oppenheimer later recalled that, while witnessing the explosion, he thought of a verse from a Hindu holy book, the ''Bhagavad Gita'' (XI,12): Years later he would explain that another verse had also entered his head at that time: John R. Lugo was flying a U.S. Navy transport at , east of Albuquerque, en route to the west coast. "My first impression was, like, the sun was coming up in the south. What a ball of fire! It was so bright it lit up the cockpit of the plane." Lugo radioed Albuquerque. He got no explanation for the blast but was told, "Don't fly south." File:Trinity-ground-zero-men-in-crater.jpg, Ground zero after the test File:Trinity Test Fireball 25ms.jpg, The ''Trinity'' explosion, 25 ms after detonation. The viewed fireball hemisphere's highest point in this image is about high. File:Trinity crater (annotated) 2.jpg, An aerial photograph of the Trinity crater shortly after the test


Instrumentation and measurements

The T (Theoretical) Division at Los Alamos had predicted a yield of between . Immediately after the blast, two lead-lined
M4 Sherman The M4 Sherman, officially medium tank, M4, was the medium tank most widely used by the United States and Western Allies in World War II. The M4 Sherman proved to be reliable, relatively cheap to produce, and available in great numbers. I ...
tanks made their way to the crater. Nuclear weapon yield, Radiochemical analysis of soil samples that they collected indicated that the total yield (or energy release) had been around . This method turned out to be the most accurate means of determining the efficiency of a nuclear explosion and was used for many years after. The energy of the blast wave was measured by a large number of sensors using a variety of physical principles. The piezoelectric blast gauges were thrown off scale and no records were obtained. The excess-velocity blast-yield measurement (precise measurement of the velocity of sound at the site of the explosion and then comparing it with the velocity of the blast wave) provided among the most accurate measurements of the blast pressure. Another method was to use the aluminum diaphragm box gauges designed to record the peak pressure of the blast wave. These indicated a blast energy of ± . They were supplemented by a large number of other types of mechanical pressure gauges. And only one of them gave a reasonable result of about . Fermi prepared his own experiment to measure the energy that was released as blast. He later recalled: There were also several gamma ray and neutron detectors; few survived the blast, with all the gauges within of ground zero being destroyed, but sufficient data were recovered to measure the gamma ray component of the ionizing radiation released. Some fifty different cameras had been set up, taking motion and still photographs. Special Fastax cameras taking 10,000 frames per second would record the minute details of the explosion. Spectrograph cameras would record the wavelengths of light emitted by the explosion, and pinhole cameras would record gamma rays. A rotating drum spectrograph at the station would obtain the spectrum over the first hundredth of a second. Another, slow recording one would track the fireball. Cameras were placed in bunkers only from the tower, protected by steel and lead glass, and mounted on sleds so they could be towed out by the lead-lined tank. Some observers brought their own cameras despite the security. Segrè brought in Jack Aeby with his 35 mm Perfex 44. He took the only known well-exposed color photograph of the detonation explosion. The official estimate for the total yield of the Trinity bomb, which includes the energy of the blast component together with the contributions from the bhangmeter, explosion's light output and both forms of ionizing radiation, is , of which about was contributed by fission of the plutonium core, and about was from fission of the natural uranium tamper. A re-analysis of data published in 2021 put the yield at . As a result of the data gathered on the size of the blast, the detonation height for the bombing of Hiroshima was set at to take advantage of the Mach stem blast reinforcing effect. The final Nagasaki burst height was so the Mach stem started sooner. The knowledge that implosion worked led Oppenheimer to recommend to Groves that the uranium-235 used in a Little Boy gun-type weapon could be used more economically in a Fat Man implosion-type weapon containing a pit (nuclear weapon), composite core with plutonium and enriched uranium. It was too late to do this with the first Little Boy, but the composite cores would soon enter production.


Civilian detection

The light from the test was visible as far as Amarillo, Texas, and a mountain range away from Trinity. The Second Air Force issued a press release with a cover story that Groves had prepared weeks before, which described the explosion as the accidental destruction of a Magazine (artillery), magazine on the base. The press release, written by Laurence, stated: Laurence had prepared four releases, covering outcomes ranging from a cover story for a successful test (the one which was used) to catastrophic scenarios involving serious damage to surrounding communities, evacuation of nearby residents, and a placeholder for the names of those killed. As Laurence was a witness to the test, he knew that the last release, if used, might be his own obituary. A newspaper article published the same day stated that "the blast was seen and felt throughout an area extending from El Paso, Texas, El Paso to Silver City, New Mexico, Silver City, Gallup, New Mexico, Gallup, Socorro, and Albuquerque, New Mexico, Albuquerque." The articles appeared in New Mexico, but East Coast newspapers ignored them, and local residents who saw the light accepted the cover story. Information about the Trinity test was made public shortly after the bombing of Hiroshima. The Smyth Report, released on August 12, 1945, gave some information on the blast, and the edition released by Princeton University Press a few weeks later incorporated the War Department's press release on the test as Appendix 6, and contained the famous pictures of a "bulbous" Trinity fireball.


Official notifications

The results of the test were conveyed to Secretary of War Henry L. Stimson at the Potsdam Conference in Germany in a coded message from his assistant George L. Harrison: The message arrived at the "Little White House" in the Potsdam suburb of Babelsberg and was at once taken to Truman and Secretary of State James F. Byrnes. Harrison sent a follow-up message which arrived on the morning of July 18: Because Stimson's summer home at Highhold was on Long Island and Harrison's farm near Upperville, Virginia, this indicated that the explosion could be seen away and heard away. Three days later, on July 21, a 13-page report written by Groves arrived at Potsdam via a courier. It stated: It continued on to estimate the yield of the test (15-20 kilotons) and describe the effects vividly. Stimson took the report to Truman, who was "tremendously pepped up by it." Winston Churchill, who observed Truman's newly confident approach with the Soviets the same day, concluded that he had become "a changed man" as a result of the news.


Fallout

Film badges used to measure exposure to radioactivity indicated that no observers at N-10,000 had been exposed to more than 0.1 roentgen (unit), roentgens (half of the National Council on Radiation Protection and Measurements recommended daily radiation exposure limit), but the shelter was evacuated before the radioactive cloud could reach it. The explosion was more efficient than expected, and the thermal updraft drew most of the cloud high enough that little fallout fell on the test site. Nevertheless, the fission consumed only out of the of plutonium, leaving to be spread through the atmosphere and as fallout. The crater was far more radioactive than expected due to the formation of trinitite, and the crews of the two lead-lined Sherman tanks were subjected to considerable exposure. Anderson's dosimeter and film badge recorded 7 to 10 roentgens, and one of the tank drivers, who made three trips, recorded 13 to 15 roentgens. The heaviest fallout contamination outside the restricted test area was from the detonation point, on Chupadera Mesa. The fallout there was reported to have settled in a white mist onto some of the livestock in the area, resulting in local beta burns and a temporary loss of dorsum (anatomy), dorsal or back hair. Patches of hair grew back discolored white. The Army bought 88 cattle in all from ranchers; the 17 most significantly marked were kept at Los Alamos, while the rest were shipped to Clinton Engineer Works, Oak Ridge for long-term observation. Dose reconstruction published in 2020 under the auspices of the National Cancer Institute documented that five counties in New Mexico experienced the greatest radioactive contamination: Guadalupe County, New Mexico, Guadalupe, Lincoln County, New Mexico, Lincoln, San Miguel County, New Mexico, San Miguel, Socorro County, New Mexico, Socorro, and Torrance County, New Mexico, Torrance. People living in the surrounding area near the site were unaware of the project and later not included in the 1990 Radiation Exposure Compensation Act support for affected "downwinders" which addressed serious community health problems resulting from similar tests conducted at the Nevada Test Site. Efforts in Congress to add the New Mexico residents to the population covered by the bill continued in 2024. In August 1945, shortly after the bombing of Hiroshima, the Kodak Company observed autoradiograph, spotting and fogging (photography), fogging on its film, which was at that time usually packaged in cardboard containers. J. H. Webb, an employee of the Kodak Company, studied the matter and concluded that the contamination must have come from a nuclear explosion somewhere in the United States. He discounted the possibility that the Hiroshima bomb was responsible because of the timing of the events. A hot spot of fallout contaminated the river water that a paper mill in Indiana used to manufacture the paper pulp, cardboard pulp from corn husks. Originally published under the title "Worse Than We Knew". Aware of the gravity of his discovery, Webb kept this secret until 1949. This incident, along with the next continental US tests in 1951, set a precedent. In subsequent atmospheric nuclear tests at the Nevada Test Site, United States Atomic Energy Commission officials gave the photographic industry maps and forecasts of potential contamination, as well as expected fallout distributions, which enabled them to purchase uncontaminated materials and take other protective measures.


Site today

In September 1953, about 650 people attended the first McDonald Ranch House, Trinity Site open house. Visitors to a Trinity Site open house are allowed to see the ground zero and McDonald Ranch House areas. More than seventy years after the test, residual radiation at the site was about ten times higher than normal background radiation in the area. The amount of radioactive exposure received during a one-hour visit to the site is about half of the total radiation exposure which a U.S. adult receives on an average day from natural and medical sources. On December 21, 1965, the Trinity Site was declared a
National Historic Landmark A National Historic Landmark (NHL) is a National Register of Historic Places property types, building, district, object, site, or structure that is officially recognized by the Federal government of the United States, United States government f ...
district, and and on October 15, 1966, it was listed on the
National Register of Historic Places The National Register of Historic Places (NRHP) is the Federal government of the United States, United States federal government's official United States National Register of Historic Places listings, list of sites, buildings, structures, Hist ...
. The landmark includes the base camp where the scientists and support group lived, ground zero where the bomb was placed for the explosion, and the McDonald ranch house, where the plutonium core to the bomb was assembled. One of the old instrumentation bunkers is visible beside the road just west of ground zero. An inner oblong fence was added in 1967, and the corridor barbed wire fence that connects the outer fence to the inner one was completed in 1972. The Trinity monument, a rough-sided, lava-rock obelisk about high, marks the explosion's hypocenter. It was erected in 1965 by Army personnel using local rocks taken from the western boundary of the range. A special tour of the site on July 16, 1995 (marking the 50th anniversary of the Trinity test) attracted 5,000 visitors. Since then, the site has been open to the public on the first Saturdays of April and October.


Gallery

File:1995 Trinity Site.jpg, Visitors to the Trinity site in 1995 for the 50th anniversary File:TrinitySiteHistoricalMarkerHighwaySign.jpg, Trinity Site Historical Marker, 2008 File:Trinity Site - Remnants of Jumbo - 2010.jpg, Remnants of Jumbo, 2010 File:Trinitite-detail3.jpg, Trinitite File:Closeup of Plaque on Monument at Trinity Site.jpg, Closeup of plaque on obelisk, 2018 File:Trinitite Display at Trinity Site Open House.jpg, Trinitite display table, 2018 File:Sign Prohibiting Removal of Trinite at Ground Zero.jpg, Sign warning against removal of trinitite, 2018 File:Crowds gathering around the Ground Zero Obelisk at Trinity Site.jpg, People gather around Ground Zero monument, 2018 File:Post-WW II Atomic Bomb Casing Almost Identical to the Fatman Bomb Casing Used Over Nagasaki.jpg, Post World War II Fat Man casing


In popular culture

The Trinity test has been portrayed in various forms of media, including documentary films and dramatizations. In 1946, an 18-minute documentary titled ''Atomic Power (film), Atomic Power'' was produced by Time Inc. under ''The March of Time'' banner and released theatrically. It featured many people involved with the project, including J. Robert Oppenheimer and Ernest Lawrence, as actors in re-creations of real discussions and events that led up to the Trinity test. In 1947, a docudrama titled ''The Beginning or the End'' chronicled the development of nuclear weapons and portrayed the Trinity test. In 1980, a television drama miniseries titled ''Oppenheimer (TV series), Oppenheimer'', a co-production between the BBC, British Broadcasting Corporation and the American television station WGBH-TV, aired for seven episodes on BBC Two. The Trinity test is depicted in its fifth episode. In early 1981, a documentary titled ''The Day After Trinity'' was released, focusing closely on the events of the Trinity test. In 1989, a feature film titled ''Fat Man and Little Boy (film), Fat Man and Little Boy'' depicted the Trinity test. Two documentaries, ''Trinity and Beyond'' and ''The Bomb (film), The Bomb'', were released in 1995 and 2015 respectively. The 2017 Twin Peaks season 3, third season of ''Twin Peaks'' prominently features a fantastical depiction of the Trinity test as part of a flashback (narrative), flashback in its Part 8 (Twin Peaks), eighth episode, providing an oblique origin story for the show's main antagonist, Bob (Twin Peaks), BOB. The 2023 Christopher Nolan-directed blockbuster ''Oppenheimer (film), Oppenheimer'' prominently portrayed the Trinity test. Nolan cited the film's depiction of the test firing as one of its most important scenes, calling it "the fulcrum that the whole story turns on." Nolan avoided using computer-generated imagery for the re-enactment of the explosion, instead using practical effects, with a smaller explosion made of gasoline, propane, aluminum powder, and magnesium being conducted and then spliced via forced perspective to recreate the size of the Trinity explosion. The popularity of the film brought newfound attention to previous media depictions of the Trinity test, such as ''The Day After Trinity''.


Notes


Citations


References

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *


External links


"Trinity and Beyond"
published August 2024 in
National Security Science
' magazine
The Trinity test
on the Sandia National Laboratories website
Trinity Remembered: 60th Anniversary


information from the National Park Service, NPS, including a link for the public open house(s)
Trinity Test Fallout Pattern




report of a visit to the Trinity site, with pictures comparing its past with its present state

Short article by Ker Than at ''3 Quarks Daily''
"War Department release on New Mexico test, July 16, 1945"
from the Smyth Report, with eyewitness reports from Groves and Farrell (1945) * *
Trinity's cloud (1945)
photographs of mushroom cloud
Video of the site, original blast, and the ranch where the bomb was assembled
from 2017 * * Rice, James. ''Downwind of the Atomic State: Atmospheric Testing and the Rise of the Risk Society''. (New York University Press, 2023): https://nyupress.org/9781479815340/downwind-of-the-atomic-state/
"The Road to Trinity"
published September 2020
Los Alamos National Laboratory: The Vault
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